Keyboards form an interface between an operator of equipment (such as chemical processing equipment, numerically controlled machine tools, computers etc.) and the equipment, which allow the operator to manually enter commands and/or data. Commands cause the equipment to operate in a particular manner. Data is mathematically manipulated by the equipment. The result of the manipulation may be used to control a display or used to create signals for controlling associated equipment such as chemical processing equipment, machine tools, laboratory test equipment, etc.
In the past, most keyboards included discrete keys overlying switch elements such that an associated switch element is closed each time a key is depressed. The main disadvantage of such "discrete" keyboards is the high production cost associated with their inclusion of mechanical mechanisms that support discrete key elements in a manner that allows the keys to be rapidly actuated.
More recently, keyboards formed of an overlay positioned atop the switch elements have been developed. When a "key" area of the overlay is depressed, the underlying switch element is actuated. Such keyboards are commonly referred to as "membrane" keyboards. The major advantage of membrane keyboards over discrete keyboards is their substantially lower production cost. On the other hand, even advanced versions of membrane keyboards, which include a dome that generates an audible "click" and produces a slight tactile sensation when a key is actuated, have disadvantages. Specifically, membrane keyboards have the disadvantage that they are difficult to use rapidly. That is, experience has shown that discrete keyboards can be manually operated more rapidly than membrane keyboards. As a result, discrete keyboards are more desirable for use in high speed data entry environments than membrane keyboards and membrane keyboards are more desirable in slower speed data and command entry environments where keyboard cost is a significant concern. The present invention is directed to providing a combination keyboard that takes advantage of the desirable attributes of both types of keyboards.